The present invention relates to the manufacture of a semiconductor device and in particular to a method of fabricating a bottle trench in a semiconductor substrate for formation of a capacitor in dynamic random access memory (DRAM).
As the integration density of dynamic random access memory (DRAM) steadily increases, reduced memory cell size is necessary. The memory cell size is primarily determined by the minimum resolution dimensions of a lithographic technique, the overlay tolerance between the different features and the layout of these features. At the same time, it is necessary to maintain the minimum required storage capacitance to reliably operate the DRAM. To meet both the cell size and storage capacitance requirements, a trench capacitor has been invented; the simple single device/capacitor memory cell has been altered to provide a vertical trench capacitor. In such designs, the capacitor is formed in a trench in the surface of the semiconductor substrate.
Since each DRAM cell only requires a transistor and a capacitor, high integration for DRAM can be accomplished as compared with other memories, such that DRAMs are widely employed in computer and electronic products.
However, as the size of a DRAM is scaled down by a factor of f (feature size), the trench storage node capacitance decreases by a factor of f. Therefore, it is important to develop methods to increase storage capacitance. One method employed to increase capacitance is to widen the lower portion of a trench, thus, increasing the surface area and creating a “bottle shaped” capacitor.